Advances in Powder Injection Molding Dr.liang

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1 Advances in Powder Injection Molding Dr.liangContentsIntroductionDevelopment process of PIMPowder for PIM and its latest advancesBinder for PIM and its latest advancesFeedstock preparation and its basic requirementsOutlines of injection moldingOutlines of debindingMaterials fabricated by PIM and Their ApplicationsPIM EconomicsPIM in China

6 Advances in Powder Injection Molding Dr.liang1. IntroductionPowder injection molding (PIM) is a very attractive near net manufacturing process, in which, a high concentration of powder is mixed with a polymer binder to form a moderate viscosity blend, called feedstock; then, the feedstock is injected into a close die cavity on equipment that is very similar to that used for polymer injection molding to form a green part; then a heat treatment, called debinding, is given to extract the binder from the component. Finally, the debinded component is sintered to form the part.

7 Advances in Powder Injection Molding Dr.liangThe main key features for PIMlow production costs,shape complexity,tight tolerances,applicability to various materials,high final properties.

8 Advances in Powder Injection Molding Dr.liangThe applications of the PIM products are very wide , range from computer heat sinks to sport components. The use of PIM for the higher temperature materials is becoming more and more attractive, because there is no competition from casting and other forming technologies .

9 Advances in Powder Injection Molding Dr.liang2. Development process of PIMThe original traces (up to the 1920's ), used a similarmethod to produce ceramic spark plug.At the end of 1950's, a lot of cemented carbidesdemonstration components were formed .In the late 1980's ,it was used more and more widelyIn the world wide, there are more than 200 companieswhich are offering PIM services.

11 Advances in Powder Injection Molding Dr.liang3. Powder for PIM and its latest advances.The first thing for PIM is powder selection, which will determine the product quality and process efficiency. The fine powder can aid sintering. Many fine powders that are candidates for PIM are agglomerated, hence they must be deagglomerated before mixing with the binder. The ideal features of PIM powders are outlined in Table 1 , and a few example powders are listed in Table 2 in detail for particle size, packing density, and angle of repose. Several new technologies developed in 1980s and 1990s could produce these powders, like high pressure water atomization , high pressure gas atomization , and NANOVAL processand so on .

14 Advances in Powder Injection Molding Dr.liang4. Binder for PIM and its latest advancesAnother important thing is binder selection. The most commonbinders are thermoplastics, such as wax or polyethylene.They usually consist of two or three components.An example binder which consists of 65% paraffin wax, 30 %polypropylene , and 5% stearic; binder content is usually near 40vol.% of the mixture.Other binder systems are used, but this binder has proven effective enough for PIM processing of many powder .

15 Advances in Powder Injection Molding Dr.liang4. Binder for PIM and its latest advancesIn 1990s, many chemical companies have fabricated very new binders or feedstock systems tailored to PIM, and the offerings include the following: acetal-based system from BASF, water-gelation system from Allied-Signal, water-soluble wax from Hoechst, silicate binder from Bayer, acrylic-based system from Rohm-Hass, and wax-polymer systems from several other companies.

17 Advances in Powder Injection Molding Dr.liang5. Feedstock preparation and its basic requirementsA successful feedstock should balance several considerations.to be sufficient to fill all voids between particles,to lubricate particle sliding during injection moldingtoo much binder is also undesired since component shape might be lost during binder removal process.the powder loading to be optimizedsince too high powder loading will result in a high viscosity and insufficient binder to fill all void space between the particles. Consequently, it is hard to mold such a feedstockthe viscosity to be similar to that of toothpaste ..

19 Advances in Powder Injection Molding Dr.liang5. Feedstock preparation and its basic requirementshomogeneityMany defects in injection molding are resulted from the inhomogeneity of the feedstock , thus, a high shear is required in mixing to force the binder among all particles.

20 Advances in Powder Injection Molding Dr.liang6.Outlines of injection moldingThe pelletized feedstock is heated in the molding machine and becomes a viscous fluid with a low enough viscosity.By injecting, the fluid flows into the die cavity and fill it out.Cooling channels in the die extract heat and solidify the polymer to preserve the molded shape.

21 Advances in Powder Injection Molding Dr.liang6.Outlines of injection moldingThe equipment is the same as used for plastic injection molding. Most common equipment is a reciprocation screw-molding machine.

22 Advances in Powder Injection Molding Dr.liang6.Outlines of injection moldingMolding pressure is very important parameters, which is determine by several factors. But normally it might be 60 MPa or more. Pressure is kept on the feedstock until the gate freezes to reduce the formation of sink marks and shrinkage voids. After totally freezing in the die, the component is ejected and one cycle of PIM is completed.

23 Advances in Powder Injection Molding Dr.liang7.Outlines of debindingUsually the binder is removed from the component. The conventional method was thermal debinding. The component is slowly heated to decompose the binder.

24 Advances in Powder Injection Molding Dr.liang7.Outlines of debindingIn the late of 1980's, a more effciently solvent debinding technology was developed in which the component was immersed in a solvent that dissolves part of the binder, leaving some polymer behind to hold the particles in place for subsequent handling. The remaining binder is thermally extracted as part of the sintering cycle.

25 Advances in Powder Injection Molding Dr.liang7.Outlines of debindingNewer binders are water soluble, so the debinding solvent is water. A more popular alternative option involve catalytic phase erosion of the binder with very high speed, which was developed in 1990's in Germany (BASF). Most of the binder is attacked by a catalytic vapor, with the residual binder removed during sintering.

26 Advances in Powder Injection Molding Dr.liang8.Materials fabricated by PIM and Their Applications.In general, most of the classic engineering materials are available except aluminum, glass, lead, and tin.Typically ferrous alloys and alumina-based ceramics are used most often. For the stainless steels, the 316L composition is used frequently, because of its combined strength and corrosion resistance.

27 Advances in Powder Injection Molding Dr.liang8.Materials fabricated by PIM and Their Applications.Other compositions that have high levels of molybdenum (up to 6%), chromium (up to 22%), or silicon (up to 3%) are also preferred.Stainless steels, iron-nickel compositions, and alumna represent the largest materials.Much of the growth in the recent years is in higher temperature materials or in very hard materials that cannot be fabricated by casting.

30 Advances in Powder Injection Molding Dr.liangFrom the table, it can been seen that the mechanical properties attainable with PIM are generally equivalent to those possible via other powder production routes.In some specific cases, the corrosion resistance of the PIM products, like the stainless steel is much more concerned. If without contamination, the PIM products are with good corrosion resistance, and often superior to the wrought products. With the developments of PIM, the PIM products got more and more wildly applications. Table 5 listed the existed applications and new possible applications .

32 Advances in Powder Injection Molding Dr.liangFrom the table, it can been seen that the recent interest has been diverted to PIM with a high aesthetic value, like running shoe cleats, golf clubs, eyeglasses, handguns and also including wrist watches.Wristwatch production via PIM is widespread, with stainless injection molded and nitrided as part of the sintering cycle to form a gold color. A significant trend in the PIM industry is developing sporting equipment. This will be a large application area and has been the basis for creation several new companies with much current research emphasis on titanium.

33 Advances in Powder Injection Molding Dr.liangAnother growth area is in microelectronic applications. Components range from computer and printer parts to semiconductor packages. The materials for these applications include Mo-Cu, AlN, invar, and W-Cu. Potential applications are in future telecommunications and avionic systems.Cemented cutting tools are another application field. One early example was specialty wood cutting routers. Other applications include cutting blades, strainers, router bits, drills, and so on. Now days, tool steels are just emerging and will be one of the next major application areas for PIM.

34 Advances in Powder Injection Molding Dr.liang9. PIM EconomicsIn principle, most products produced by conventional metallurgy method can be fabricated by PIM process. In spite of these, there are several key factors in determining the feasibility of PIM product.The critical factors are part complexity and production cost, especially the cost of the PIM product, which is determined by the tool cost, powder cost, labor rates et al. Now days, the PIM market was located in the high production quantities for complex parts where the typical cost can be reduced 20-30% as compared with other alternative production process.

35 Advances in Powder Injection Molding Dr.liang9. PIM EconomicsFor PIM economics, another topics discussed frequently is the size of the market. The investigation showed that the total world wide sales for PIM was about 45 million during the late 1980's, $230 million by1993 and $378 million in 1996, out of which 60% were from metals, 35% from ceramics, and 5% from carbides. By geographic partitioning the guess is that two- thirds of the world wide sales were in USA, 20% in Asia (especially in Japan), 12%in Europe, According to the estimation, the current growth rate in sales are at 22% per year.

36 Advances in Powder Injection Molding Dr.liang9. PIM EconomicsBasically speaking, the PIM market has come of age during 1980's. Now days, most of the current interest stems from the success of metal injection molding (MIM). However, the largest production operations are focused on ceramics, largely for casting cores, automotive sparkplugs and oxygen sensors, industrial ceramics, steel melting refractories, and high performance ceramics. On the other hand, the number of companies practicing MIM is larger, but they are smaller operations. Today, PIM is an accepted material shaping technique. The process currently has many applications and is making inroads against investment casting, especially for small products.

37 Advances in Powder Injection Molding Dr.liang10.PIM in ChinaIn China, universities, Institutes and companies started their PIM researches and production during 1950's. At that time, a few ceramic PIM products, like alumina spark plugs, were produced. The fundamental researches were focused on the powder selection, binder design and rheological evaluation, and dimensional accuracy control.

38 Advances in Powder Injection Molding Dr.liang10.PIM in ChinaIn 1980's, the advanced research project for the use of high performance ceramics in heat engine was conducted in a few key universities (like Qing hua University) and key Labs(like…). The PIM production of dense silicon nitride, silicon carbide and toughened zirconia components was being extensively investigated. The complex-shaped components included radial rotors, vanes, turbocharging rotors, were produced by PIM methods. Beside the further fundamental researches, the in situ studies, injection molding controlling and flow stimulation have been developed.

39 Advances in Powder Injection Molding Dr.liang10.PIM in ChinaIn 1990's, more and more universities and institutes were involved in metal injection molding. Several MIM Lab were established, such as MIM Lab in the National Key Lab of Powder Metallurgy of Central South University(CSU) . Under the finical support of Nature Science Foundation of China, 863 High-tech Agency of China, a lot fundamental and applied researches have been conducted. Many applied are associated with specific application such as wristwatches, tungsten penetrators, gun parts. Materials included tool steel, tungsten alloys, cemented carbide, stainless steel, titanium, The developing technologies include new powder production techniques, new binder system design. On the basis of these ten years research achievement, one PIM production line with $5million annual outputs has been constructed in 1999 at National Key Lab for Powder Metallurgy of CSU.

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